Targeting spam control on middleboxes: Spam detection based on layer-3 e-mail content classification

This paper proposes a spam detection technique, at the packet level (layer 3), based on classification of e-mail contents. Our proposal targets spam control implementations on middleboxes. E-mails are first pre-classified (pre-detected) for spam on a per-packet basis, without the need for reassembly. This, in turn, allows fast e-mail class estimation (spam detection) at receiving e-mail servers to support more effective spam handling on both inbound and outbound (relayed) e-mails. In this paper, the naïve Bayes classification technique is adapted to support both pre-classification and fast e-mail class estimation, on a per-packet basis. We focus on evaluating the accuracy of spam detection at layer 3, considering the constraints on processing byte-streams over the network, including packet re-ordering, fragmentation, overlapped bytes, and different packet sizes. Results show that the proposed layer-3 classification technique gives less than 0.5% false positive, which approximately equals the performance attained at layer 7. This shows that classifying e-mails at the packet level could differentiate non-spam from spam with high confidence for a viable spam control implementation on middleboxes.     

A hierarchical design methodology for full-search block matching motion estimation

Many useful DSP algorithms have high dimensions and complex logic. Consequently, an efficient implementation of these algorithms on parallel processor arrays must involve a structured design methodology. Full-search block-matching motion estimation is one of those algorithms that can be developed using parallel processor arrays. In this paper, we present a hierarchical design methodology for the full-search block matching motion estimation. Our proposed methodology reduces the complexity of the algorithm into simpler steps and then explores the different possible design options at each step. Input data timing restrictions are taken into consideration as well as buffering requirements. A designer is able to modify system performance by selecting some of the algorithm variables for pipelining or broadcasting. Our proposed design strategy also allows the designer to study time and hardware complexities of computations at each level of the hierarchy. The resultant architecture allows easy modifications to the organization of data buffers and processing elements-their number, datapath pipelining, and complexity-to produce a system whose performance matches the video data sample rate requirements.     

A spam rejection scheme during SMTP sessions based on layer-3 e-mail classification

This paper proposes a scheme that rejects spam e-mails during their simple mail transfer protocol (SMTP) sessions. This scheme utilizes a layer-3 e-mail classification technique, which allows e-mail classes to be estimated before the end of SMTP sessions at receiving e-mail servers. We analyze the proposed scheme using discrete-time Markov chain analysis under varying e-mail traffic loads and service capacities. This paper also considers the effects of e-mail retransmission and illegal spam relaying by zombie systems on the performance of the proposed scheme. Results from our analysis show that e-mail server loading decreases by using the proposed technique. This allows the reduction in non-spam e-mail queuing delays and loss probability. Our scheme also protects e-mail servers from being overloaded by spam traffic and, if performed collectively over the Internet, it is capable of performing outbound spam control.     

Spectral and spatial dynamics of a multimode GaN-based blue laser diode

ABSTRACT

High-resolution spectral analysis of a multimode GaN-based blue laser diode was performed as a function of temperature and current both below and above the threshold levels. Maps of longitudinal modes evolution as a function of current and temperature were obtained from the highly resolved emission spectra of the laser diode. The evolution of emitted longitudinal modes with current and temperature exhibited redshifts at rates of 0.0059 nm/mA and 0.0149 nm/°C, respectively. Similarly, the laser gain profile was observed to shift towards longer wavelengths but with rates of 0.022 nm/mA and 0.0439 nm/°C. The longitudinal mode spacing of 0.0540 nm was experimentally evaluated and compared with its equivalent theoretically predicted value.     

Improving Networks‐on‐Chip performability: A topology‐based approach

The performability metric is commonly used in Networks‐on‐Chip (NoC)‐based systems to represent their abilities to successfully complete specific tasks in finite time intervals. In this paper, we present a novel topology‐based performability model for NoC‐based systems. The model is used to evaluate the performability of NoC‐based systems at early design phases. A comparative study of nine commonly used network architectures is performed using the proposed model. The purpose of the study is to explore the impact of the network topology on the performability of NoC‐based systems. Using the output from this study, a new methodology is proposed to improve the performability of a given application at early design phases. In this methodology, a joint consideration of five design parameters (network topology, target application traffic distribution, mapping of processing elements, noise power, and voltage swing) is carried out. Using the proposed methodology, designers can select the optimal topology for a given application that maximizes system performability. The effectiveness of the proposed methodology in determining the optimal topology is verified by experimental work and validated through a case study of a video application. Copyright © 2010 John Wiley & Sons, Ltd.     

Prioritized e‐mail servicing to reduce non‐spam delay and loss: A performance analysis

This paper proposes a prioritized e‐mail servicing on e‐mail servers to reduce the delay and loss of non‐spam e‐mails due to queuing. Using a prioritized two‐queue scheme, non‐spam e‐mails are queued in a fast queue and given higher service priority than spam e‐mails that are queued in a slow queue. Four prioritized e‐mail service strategies for the two‐queue scheme are proposed and analyzed. We modeled these four strategies using discrete‐time Markov chain analysis under different e‐mail traffic loads and service capacities. Non‐spam e‐mails can be delivered within a small delay, even under heavy e‐mail loadings and high spam‐to‐non‐spam a priori. Results from our analysis of the two‐queue scheme show that it gives non‐spam delay and loss probability two orders of magnitude smaller than the typical single‐queue approach during heavy spam traffic. Moreover, prioritized e‐mail servicing protects e‐mail servers from spam attacks. Copyright © 2007 John Wiley & Sons, Ltd.     

Power optimization for application-specific networks-on-chips: A topology-based approach

This paper analyzes the main sources of power consumption in Networks-on-Chip (NoC)-based systems. Analytical power models of global interconnection links are studied at different levels of abstraction. Additionally, power measurement experiments are performed for different types of routers. Based on this study, we propose a new topology-based methodology to optimize the power consumption of complex NoC-based systems at early design phases. The efficiency of the proposed methodology is verified through a case study of an MPEG4 video application. Experimental results show a promising improvement in power consumption (8.55%), average number of hops (10.80%), and number of global links (56.25%) compared to the best known related work.     

页岩储层CO2驱沥青质沉淀特征及影响因素分析

为明确CO2在页岩储层纳米孔隙中的流动机理及其对沥青质沉淀的影响,采用自主研发的高温高压过滤容器和复合纳米滤膜,进行纳米滤膜过滤实验,模拟了单(多)层岩石切片作用下的CO2驱替过程,开展储层参数和注入参数对CO2驱替效果及沥青质沉淀的影响研究.研究结果表明:CO2驱会引发沥青质沉淀,导致剩余油中的沥青质含量远大于产出油...     

Variations in isotopic composition of desalinated water

Variations in isotopic ratios of water samples collected from three plants functioning on two different desalination processes were evaluated by comparing their measured δ¹⁸O, δ¹⁷O and the δ²H isotopic ratios before and after desalination using a system based on tunable off‐axis integrated‐cavity‐output diode laser spectroscopy (OA‐ICOS). The δ¹⁸O, δ¹⁷O and the δ²H isotopic ratio measurements for water samples collected before desalination are compared against their peers of desalinated water from two desalination plants on the Arabian Gulf that are operating under the Multistage Flash (MSF) process. Also, variations in the δ¹⁸O, δ¹⁷O and the δ²H isotopic ratio measurements due to desalination from a Reversal Osmosis (RO) facility in Dhahran, Saudi Arabia were also reported and compared against variations in isotopic composition of water desalinated in two MSF plants.